Close unclosed client sessions properly

[hynek]

What do these changes do?

ClientSession.__del__ uses a bare self.close() which causes a warning. This fixes that warning. I think this should be fine like that?

Are there changes in behavior for the user?

One warning less.

Related issue number

n/a

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[asvetlov]

It's a complex question.
__del__ is called on session destruction.
It could be even interpreter finalization stage if the session has global scope (we discourage this approach but still support it).

If the loop is closed before ClientSession.__del__ -- nothing to do.

On other hand the session could be dropped in coroutine context:

async def f():
    session = aiohttp.ClientSession()
    ...
    del session  # or just implicit decref on frame destruction

In this case the loop is running, loop.run_until_complete() is prohibited.

[hynek]

Yeah, I suspected it’s not clear cut.

I’d suggest to either drop the close altogether or wrap it in a with suppress(Exception): for an best-effort try. As it’s now it’s kind useless, isn’t it?

[asvetlov]

I think dropping is just fine.
Let's keep a warning report part but don't try to close the session: it is not very reliable.

[codecov-io]

Codecov Report

Merging #2523 into master will decrease coverage by <.01%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #2523      +/-   ##
==========================================
- Coverage   97.13%   97.13%   -0.01%     
==========================================
  Files          39       39              
  Lines        8066     8065       -1     
  Branches     1414     1414              
==========================================
- Hits         7835     7834       -1     
  Misses         99       99              
  Partials      132      132

Impacted Files	Coverage Δ
tests/autobahn/client.py	94.91% <0%> (-0.02%)	⬇️

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[asvetlov]

Thanks!
Backported to 2.3, aiohttp 2.3.3 released